What is a GPKG file?
A file with a .gpkg extension consists of a geographic information system implemented as a SQLite database container containing data and metadata tables with typical definitions, format limitations, integrity assertions and content constraints. It was published in 2014; defined by the OGC (Open Geospatial Consortium) on the behalf of the US military. Various governments, commercial, and open source organizations widely support the GeoPackage.
GPKG file format
A GeoPackage is made up as an extended SQLite 3 database file; a standard defines a set of rules (required conventions) for:
- Storing tile matrix sets of imagery
- Vector features
- Raster maps at various scales
- Metadata and schema
You can extend a GeoPackage by using the extension rules as defined in clause 2.3 of the standard. The purpose of designing a GeoPackage was to make a lightweight database as much possible and include it in a ready-to-use single file. This makes it ideal for mobile applications in off-line mode and fast sharing on cloud storage or USB storage devices, etc.
GPKG Contents
The GeoPackages contain a number of tables, like other relational databases. These tables can be either user-defined or metadata tables. GeoPackages consist of two mandatory metadata tables:
gpkg_contents
A table of contents for a GeoPackage. The mandatory columns in this table are:
- table_name: the actual name of the user-defined data table;
- data_type: the data type, e.g. titles, features and attributes;
- identifier and description: human-readable text ;
- last_change: the informational date of last change, in ISO 8601 format ;
- min_x, min_y, max_x, and max_y: the spatial extents of the content. ;
- srs_id: spatial reference system .
gpkg_spatial_ref_sys
For spatial reference content; including but not limited to tiles and features, each row in contents must reference a coordinate reference system; stored in the gpkg_spatial_ref_sys table. The mandatory columns in this table are:
- srs_name, description: a human readable name and description for the SRS;
- srs_id: a unique identifier for the SRS; also the primary key for the table;
- organization: Case-insensitive name of the defining organization.
- organization_coordsys_id: Numeric ID of the SRS assigned by the organization;
- definition: Well Known Text definition of the SRS.
